1. Field of Invention
The present invention relates to an apparatus and method for high-resolution, low-cost perimetry, and more particularly, relates to an apparatus and method for high-resolution, low-cost perimetry for improved the static and kinetic visual filed mapping.
2. Prior Art
Visual field mapping (fundus perimetry) is a psychophysical test performed by projecting small light stimuli to different locations and different perimeters of the fundus. It is commonly used in the detection, diagnosis and evaluation of several retinal, optic nerve and brain diseases, such as glaucoma, retinitis pigmentosa and stroke. The most commonly used apparatus are the photopic Goldman device which uses a manual kinetic test,1 and the photopic and scotopic Humphrey instrument which uses an automatic static test.2-5 In the static method, a dot of light is flashed at random locations onto a visual field and the patient signals when he/she sees the flash. The patient adjusts fixation between each flash by a centrally presented target. This method allows for both screening and threshold mapping. In contrast, in the kinetic method, a dot of light moves in straight lines in the visual field, and the patient signals when the dot is visible and when it disappears. During each scan, the patient is required to maintain fixation. For example, in order to test the peripheral damage caused by glaucoma, it is common to scan twelve different radial lines, equally separated by 30xc2x0. However, this technique has the limitation of indeterminacy in the precise location at which the patient has signaled, since the response delay is unknown. Therefore, the kinetic test is considered rapid but imprecise,1,6,7 and it is usually used for qualitative tests, such as depicting lines of equal sensitivity in the visual field.2 
The conventional apparatuses described above are not suitable for mapping inside the macula region, since an accurate high-resolution mapping is required. The Goldman perimeter is limited by the problem posed by the patient""s response delay and the fact that operator monitoring is done manually, while the Humphrey instrument has limitations imposed by its software implementation (the most common mapping resolution is 4xc2x0) and the resolution of the bulbs in its hemisphere. In addition, the patient""s eye movements can cause significant errors at high-resolution of less than 1xc2x0.
Severe damage to the macula often results in eccentric fixation, which is unstable in comparison with normal fixation.8-10 Studies on macular-damaged retinas have shown that more than 50% of mapping trials had a shift of up to 15 minutes of arc (0.25xc2x0) during a 400 msec flash, while 40% of trials had a shift of 1.5xc2x0 or more during a 1000 msec flash.11 Thus, the eye movements are significant enough, but still can be hardly detected by projecting to the blind spot (as it is done in the Humphrey device) since its radius is about 5xc2x0. Moreover, the blind spot""s location is shifted under eccentric fixation, causing misplacement of the estimated blind spot""s location.
The new generation of fundus perimeters enables the visualization of the retina with precise high-resolution mapping superimposed on it. The most sophisticated of them is the scanning laser ophthalmoscope (SLO).6,7,9,12-22 The SLO uses two simultaneous laser beams, an invisible infrared beam for imaging the retina, and a visible red beam for perimetry. The SLO enables automatic kinetic and static studies with a resolution of 2 minutes of arc (0.033xc2x0). The operator can see the retinal image and the fixation target during the test, and can thus compensate online for significant eye movements.9 The SLO and other advanced fundus perimeters are attractive for research, but they are still not in widespread practical use, mainly due to their high cost and cumbersome operation.
The present invention seeks to overcome the disadvantages and drawbacks of the prior art, as explained above, and provides a method and apparatus for high-resolution, low-cost perimetry, and more particularly, relates to an apparatus and method for high-resolution, low-cost perimetry for improved the static and kinetic visual filed mapping. The focus of the work leading to the present invention concerned mapping macular scotomas and checking the residual sight in them, by using common affordable tools. Thus, the main goal was to achieve low-cost high-resolution mapping with minimal eye movements error, and with results that can be automatically visualized on the fundus photograph.
The foregoing is is accomplished by the present invention by employing as the perimeter a portable computer and a projector, and using two screening methods, multi-resolution static and bi-directional kinetic. The invention as applied to a static test starts with relatively low-resolutions, and only the unseen zones are selectively remapped under higher resolutions during successive iterations. The invention as applied to a kinetic test uses a response to a continuously moving target, and the unknown response delay is compensated for by an algorithm that merges the patient""s response to measurements at the same visual location, but with opposite scanning directions. Offline visualization of the mapping results is performed automatically superimposed over the fundus image.
Other and further objects and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments when taken in conjunction with the appended drawings.